Effects of Radiation on the Olefinic Groups in Polybutadiene

Olefinic groups, present in high concentration in polybutadiene, change rapidly when exposed to ionizing radiation. Concentration changes of olefinic groups in four polybutadienes resulting from gamma and reactor irradiation were measured by infrared absorption spectra. The four types, irradiated in vacuum as x-ray-cured thin films were 92% cis-1,4, crystalline 95% trans-1,4, amorphous 73% trans-1,4, and an amorphous 71% side vinyl 1,2 polymer. The cisvinylene groups were destroyed at a rate (G value) of —15 groups per 100 e.v., with the rate of conversion to the trans isomer proceeding at G = ~ 7. The trans-vinylene and side vinyl groups were destroyed in the polymers containing appreciable concentrations of them in apparent first-order processes. Their high reaction rates indicate efficient energy or charge transfer to the olefinic groups or possibly chain reactions.